To start an engine, an engine starter using an electric motor has heretofore been used. For example, Patent Document 1 discloses an engine starter/generator that use an SR motor (Switched Reluctance Motor). In recent years, as an engine-starter motor, SR motors whose structure is simple and solid has gained attention. Especially, the use of SR motors is expanding against the backdrop of a surge in the prices of rare earths, as the motors do not employ permanent magnets in rotors. In the case of the starter/generator disclosed in Patent Document 1, the rotation shaft of a motor is connected to the crankshaft of an engine via a clutch or reducer; The starter/generator functions as a starter (power machine) when an engine is being stopped, and as a generator (power generator) after the start of the engine.